Bottle-shaped can manufacturing method and bottle-shaped can

ABSTRACT

A method for manufacturing a bottle-shaped can for holding content having strong metal corrosive properties such as sparkling wine. The method includes shaping a cap into a diametrically reduced bottomed cylindrical can body, forming a shoulder portion and a container mouth on the can body, forming a curled portion, a thread and an annular bead on the container mouth, seaming a can lid to the can trunk, and amorphizing a thermoplastic resin layer covering an inner surface of the container mouth on which the curled portion, the thread and the annular bead are formed.

TECHNICAL FIELD

The present invention relates to a method for manufacturing abottle-shaped can comprised of a can trunk, a shoulder portion and acontainer mouth formed integrally from a metal sheet. More particularly,the present invention relates to a manufacturing method of bottle-shapedcan suitable to hold a corrosive content such as sparkling wine, and thebottle-shaped can manufactured thereby.

BACKGROUND ART

In recent years, a variety of contents have been filled in thebottle-shaped can in a hermetic manner. For example, the bottle-shapedcan is filled with beverage such as mineral water, sports drink,Japanese tea, black tea, Chinese tea, coffee, carbonated drink, fruit orvegetable juice, and sold in the market. The bottle-shaped can is alsofilled with light alcohol such as beer, sour, cocktail, and sold in themarket.

Generally, corrosive subsulfate such as sodium sulfite is added tofermented fruit liquor such as wine for the purpose of avoidingoxidization. Such antioxidant may damage an inner protective coating ofthe bottle-shaped can by sulfurous acid. Therefore, if the bottle-shapedcan filled with wine or the like, corrosion resistance of thebottle-shaped can would be degraded thereby causing a corrosion of ametal surface of the can. In the worst case, a leakage of the contentmay be caused due to pitting corrosion. Thus, it is difficult to holdthe content such as wine in the bottle-shaped can unless decreasing theconcentration of sulfurous acid.

In order to solve the foregoing problem, Japanese Patent Laid-Open No.2006-264734 discloses a technique to enhance the corrosion resistance ofa bottle can made of aluminum. According to the teachings of JapanesePatent Laid-Open No. 2006-264734, an inner surface of an aluminum sheetis covered with a coating having good workability prior to forming acan, and a necking, a flanging or a threading (including a curling) areexecuted. Then, the inner surface is subjected to a second coating.However, organic solvent may affect human body during or after coating,and may pollute the environment. In addition, since the coating has tobe carried out before and after the threading, manufacturing cost of thebottle can will be raised. Therefore, it is preferable to omit the innercoating of the can body.

Japanese Patent Laid-Open No. 2006-62688 discloses a metal container forholding wine that is prevented from being corroded by sulfurous acid.According to the teachings of Japanese Patent Laid-Open No. 2006-62688,a can body is formed by drawing and ironing a metal sheet, and at leasta surface of the metal sheet to be an inner face of the container iscoated with a resin layer. In addition, an intermediate layer ofacidification agent such as calcium carbonate reacting to sulfurous acidis formed in the resin film covering the inner surface of the can.

According to the teachings of Japanese Patent Laid-Open No. 2006-62688,therefore, calcium carbonate reacts to sulfurous acid so that the canbody is prevented from being corroded by sulfurous acid and flavor ofwine held therein is prevented from being deteriorated. That is, thecorrosion of the can and the deterioration in flavor of the wine can beprevented without reducing a concentration of sulfurous acid containedin the antioxidant. In addition, since the inner face of the can body iscovered with the resin film, the organic solvent will not affect humanbody and will not pollute the environment. Therefore, the containerstaught by Japanese Patent Laid-Open No. 2006-62688 are sold in themarket.

DISCLOSURE OF THE INVENTION Technical Problem to be Solved

The bottle-shaped can is filled with the content, and an aluminumclosure is applied to a container mouth of the bottle-shaped can by aroll-on capping method disclosed e.g., in Japanese Patent Laid-Open No.2001-270596. Specifically, the closure is applied to the container mouthof the can, and the closure is pressed so that the resin liner is pushedtightly onto an opening end of the container mouth. Thereafter, a threadis rolled on a cylindrical skirt of the closure by pressing a threadroller against the cylindrical skirt, and a lower end of the cylindricalskirt is tightened by pressing a tightening roller (or a lower endtightening roller) against the lower end of the cylindrical skirt.

Given that the bottle-shaped can thus closed by the closure by theroll-on capping method is filed with wine having strong metal corrosiveproperties such as champagne or sparkling wine, the container mouth maybe corroded by wine, and such problem has not yet been solved.

Specifically, the bottle-shaped can is closed by a pilfer proof closure,and a pilfer proof band is detached from a lower end of the closure whenthe closure is unscrewed and remains around the container mouth. To thisend, the lower end portion of the closure is pressed by a plurality ofthread rollers to be contacted onto an annular bead formed on thecontainer mouth. As a result, the annular bead may be deformed and acoating layer covering an inner surface of the annular bead may bedamaged at the micro level. Therefore, the metal can body is corroded bycarbon dioxide and sulfurous acid at such defective site at the microlevel.

Thus, if the bottle-shaped can made of metal is filled with wine havingstrong metal corrosive properties such as champagne or sparkling wine,the bottle-shaped can may be corroded by carbon dioxide contained insparkling wine. Consequently, flavor of wine held in the corroded canmay be deteriorated. Therefore, the bottle-shaped can has to be improvedto hold such wine having strong metal corrosive properties.

The present invention has been conceived noting the foregoing technicalproblems, and it is an object of the present invention to provide amanufacturing method of a bottle-shaped can having excellent corrosionresistance and preserving properties to hold sparkling wine havingstrong metal corrosive properties, and a bottle-shaped can manufacturedby the method of the present invention.

Solution to Problem

In order to solve the above-explained problems, that is, in order toprevent corrosion of the metal sheet by carbon dioxide contained insparkling wine held in the bottle-shaped can, various kinds ofexperimentations have been conducted. The experimentations showed thatthe above-explained problems can be solved by heating and cooling acontainer mouth before filing the bottle-shaped can with the content, soas to amorphize an inner coating to recover elasticity and ductilitythereof. This discovery is utilized in the present invention to solvethe above-explained problems. According to one aspect to the presentinvention, there is provided a bottle-shaped can manufacturing methodcomprised of: a cup shaping step of forming a cup by punching out from ametal sheet in which a thermoplastic resin coating layer is formed on atleast a surface to be an inner face of the can and a lubricant isapplied thereto; a can trunk shaping step of shaping the cap into adiametrically reduced bottomed cylindrical can body; a container mouthshaping step of forming a shoulder portion and a container mouth bydiametrically reducing one of the end portions of the bottomedcylindrical can body; and a curling/threading/beading step of forming acurled portion on a leading end of the container mouth, and forming athread and an annular bead on the container mouth. In order to solve theabove-explained problem, the manufacturing method of the presentinvention is characterized by an amorphization step of amorphizing atleast the thermoplastic resin coating layer covering an inner surface ofthe can body in which the curled portion, the thread and the annularbead are formed on the container mouth situated above the shoulderportion, by heating at least the thermoplastic resin coating layercovering the inner surface of the can body to above a melting pointthereof, and immediately cooling the heated thermoplastic resin coatinglayer.

The container mouth shaping step includes a top dome shaping step offorming the shoulder portion and the container mouth by diametricallyreducing a bottom side of the bottomed cylindrical can body, and theamorphization step includes a step of amorphizing at least thethermoplastic resin coating layer covering the inner surface of the canbody in which the container mouth is opened and a bottom lid is seamedto a lower end of the can trunk on the side opposite to the containermouth.

The amorphization step further includes: an induction heating step ofletting the can body through an induction heating apparatus whilerotating the can body around an axis of the can; and a cooling step ofimmediately cooling the heated container mouth by immersing thecontainer mouth into a cooling water held in a cooling tank.

The cooling step includes a step of cooling the container mouth byimmersing the container mouth into the cooling water held in the coolingtank while orienting the container mouth downwardly; and theamorphization step includes a blowing step of blowing off the wateradhering to the container mouth oriented downwardly.

The amorphization step further includes a cooling step of coolingcontainer mouth of the can body conveyed in a manner to orient thecontainer mouth downwardly, by immersing the container mouth into thecooling water held in the cooling tank while inclining a center axis ofthe container mouth with respect to a water surface, and thereafterpulling the container mouth out of the cooling tank while inclining thecontainer mouth inversely to that of the case of immersing the containermouth into the cooling water.

The amorphization step further includes a cooling step of coolingcontainer mouth while circulating the cooling water in the tank at asubstantially same speed as a conveying speed of the can body and in thesame direction as a conveying direction of the can body.

According to another aspect of the present invention, there is provideda bottle-shaped can, that is formed from a metal sheet in which athermoplastic resin coating layer is formed on at least a surface to bean inner face of the can. In the bottle-shaped can of the presentinvention, a crystallinity (Cn) of the thermoplastic resin coating filmcovering an inner surface of a container mouth of the finished cansatisfies a following inequality (1):

Cn<1  (1);

where Cn is an infrared absorption intensity measured by IR spectroscopymethod (reflection infrared spectroscopy method), which can be expressedby a following expression:

Cn=(a peak height at 1340 cm⁻¹)/(a peak height at 1578 cm⁻¹).

In the bottle-shaped can of the present invention, a relation betweenthe crystallinity (Cn) of the thermoplastic resin coating film at theinner surface of the container mouth of the finished can, and acrystallinity (Cw) of the thermoplastic resin coating film at an innersurface of the can trunk satisfy a following inequality (2):

Cn/Cw<1  (2);

where Cw is an infrared absorption intensity measured by the IRspectroscopy method (reflection infrared spectroscopy method), which canbe expressed by a following expression:

Cw=(a peak height at 1340 cm⁻¹)/(a peak height at 1578 cm⁻¹).

In addition, in the bottle-shaped can of the present invention, thethermoplastic resin coating layer covering an inner surface of thecontainer mouth is subjected to an amorphization treatment to amorphizethe thermoplastic resin after forming the container mouth, by heatingthe thermoplastic resin coating layer to above a melting point thereof,and immediately cooling the heated thermoplastic resin.

Advantageous Effects of Invention

Thus, according to the manufacturing method and the bottle-shaped can ofthe present invention, at least the thermoplastic resin layer coveringthe inner surface of the container mouth is brought into non-orientationstate by heating the container mouth locally and cooling the heatedcontainer mouth immediately before filling the bottle-shaped can withthe content. Therefore, the thermoplastic resin layer is brought intonon-orientation amorphous state thereby recovering defective sites ofthe layer at the micro level caused during forming the container mouthcan be recovered. In addition, elasticity and ductility of thethermoplastic resin layer can be improved. Consequently, impactresistance of the thermoplastic resin layer covering the inner surfaceof the can body can be enhanced at the portion contacted with atightening roller during capping (e.g., an annular beads). For thisreason, damages of the thermoplastic resin layer covering the innersurface of the annular beads can be minimized so that corrosionresistance of the bottle-shaped can against sparkling wine is improved.Thus, the bottle-shaped can according to the present invention isallowed to be filled with various kinds of contents including sparklingwine having strong metal corrosive properties.

As described, only the container mouth situated above the shoulderportion is heated at the amorphization step after forming the curledportion, the thread and the annular bead on the container mouth.Therefore, at least the thermoplastic resin layer covering the innersurface of the container mouth can be amorphized while maintaining abuckling strength of the can body against a capping pressure. That is, afilling step and a seaming step are allowed to be carried out withoutmodifying an existing capping apparatus significantly. Thus, the presentinvention is economically viable.

In addition, since the amorphization step is carried out after seaming abottom lid to the can body, a sealing rubber of the bottom lid will notbe heated to generate an offensive odor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing one example of the bottle-shaped can towhich the present invention is applied.

FIG. 2 is a process diagram for explaining a manufacture process formanufacturing the bottle-shaped can according to the present invention.

FIG. 3 is a sectional close-up view of the container mouth of thebottle-shaped can shown in FIG. 1.

FIG. 4 is a view schematically showing a deformation of the annular beadduring the capping of the manufacturing method according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, a preferred example of the presentinvention will be explained hereinafter.

[As to a can Body of the Bottle-Shaped Can]

One example of the bottle-shaped can formed by the manufacturing methodof the preferred example is shown in FIG. 1. The bottle-shaped can 1 iscomprised of a diametrically large cylindrical can trunk 2, adome-shaped shoulder portion 3 having an arcuate cross-section situatedabove the can trunk 2, a diametrically small container mouth 4 formedintegrally with the shoulder portion 3, and a bottom lid 5 seamed to alowest end of the can trunk 2 to close an opening. In addition, adesired printing design (e.g., patterns and/or letters) is applied to amajor part of an outer surface of the can trunk 2 including the shoulderportion 3 shadowed in FIG. 1.

FIG. 2 schematically shows a process for manufacturing the bottle-shapedcan 1 shown in FIG. 1 having the bottom lid. According to the method ofthe preferred example, the bottle-shaped can 1 is formed from a metalsheet prepared by forming a thermoplastic resin coating layer in anamorphous state on both side, and applying lubricant to the coatinglayers (i.e., a laminated sheet). First of all, a disc-shaped blank ispunched out from the laminated metal sheet material at a cup shapingstep. Then, the disc-shaped blank is shaped into a cup by a drawingtreatment. At a subsequent can trunk shaping step, at least one or moretimes of re-drawing and an ironing are applied to the cup therebyforming a diametrically reduced bottomed cylindrical can body having athinned can trunk.

Then, an open end of the can is trimmed to a predetermined length at atrimming step. The cup thus trimmed is transferred to a printing/coatingstep, as the customary way of manufacturing a two-piece can. At theprinting/coating step, a desired printed decoration (e.g., patternsand/or letters) is printed on the cylindrical can trunk 2. Then, theprinted face is coated with a top coating layer, and the printed inklayer and the top coating layer are cured or dried sufficiently at adrying step.

The can trunk 2 of the bottomed cylindrical can is thus printed (and topcoating is applied) is further transmitted to a container mouth shapingstep or a top dome shaping step. At the top dome shaping step, thebottom side corner portion (i.e., the bottom portion and the can trunk 2near the bottom) of the bottomed cylindrical can including the printedportion of the can trunk 2 is preliminarily shaped into a curvedshoulder face whose longitudinal section is arcuate, and then, of thedrawing is applied to the bottom side of the can plural times tocomplete the shoulder portion 3 and to form the unopened container mouth4.

The can thus prepared is heated by a known heating means such as afurnace and a heating oven so that at least the thermoplastic resincoating layer covering the inner surface of the can is adhered to themetal can surface. At subsequent threading, curling, and bead formingsteps, first of all, the leading end of the unopened container mouth 4is cut out to be opened. Then, as illustrated in the partial sectionalview of FIG. 3, an open end portion 11 is curled outwardly to form anannular curled portion 12, and a thread 13 on which the closure isscrewed is formed around cylindrical container mouth 4. Further, annularbeads 14 and 15 are formed below the thread 13.

Specifically, a concave bead 15 is formed by depressing the containermouth 4 radially inwardly below the thread 13, and as a result, a convexbead 14 is formed above the concave bead 15. An after-mentionedpilfer-proof band of the closure is pushed tightly onto an inclined face14 a between the beads 14 and 15.

At a subsequent necking/flanging step, a necking-in and a flanging aresequentially applied to an lower open end portion of the can trunk 2 onthe opposite side of the container mouth 4. Then, at a can lid seamingstep, a separate bottom lid made of metal is seamed to the flangeportion formed on the lower opening portion of the can trunk 2 by adouble-seaming method using a (not-shown) seamer (i.e., a can lidseaming machine).

However, a molding strain of the thermoplastic resin coating layer maybe caused in the container mouth 4 of the can body as a result ofsubjecting the can body to the foregoing threading, curling, and beadforming steps. Therefore, if a the bottle-shaped can 1 is subjected to aroll-on process to push a skirt portion of the closure mounted on thecontainer mouth 4, a coating layer covering an inner surface of thecontainer mouth 4 may be damaged. As shown in FIG. 4, a tighteningroller of a capping apparatus is brought into contact with the concavebead 15 through a closure applied to the container mouth 4 while rollingaround the container mouth 4 plurality of times to push a lower end ofthe closure onto the inclined face 14 a. Consequently, the concave bead15 is deformed inwardly and a thickness thereof is thinned.Specifically, such capping is executed by a plurality of rollers(basically 2 to 3 rollers). Therefore, given that a thickness of theresin coated metal sheet is thinner than 0.3 mm, the concave bead 15 maybe thinned while being deformed into an oval or elliptical shape. As aresult, the concave bead 15 may remain deformed and a diameter of thecontainer mouth 4 may be reduced approximately 0.1 to 0.4 mm from theoriginal diameter. Therefore, the thermoplastic resin coating layer (oran adhesive layer) covering the inner surface of the concave bead 15 maybe thinned and weakened locally by a compression stress and a tensilestrength thereby developing defects at the micro level. Such defectivesites at the micro level can be found only after storing thebottle-shaped can filled with the contents and closed by the closure fora certain period of time. The bottle-shaped can 1 thus having thedefects at the micro level on the thermoplastic resin coating layer willnot especially be corroded even if it is filled with the contents suchas soft drink including mineral water, sports drink, tea, coffee,carbonated drink and fruit or vegetable juice etc., and alcoholicbeverages including beer, cocktail etc. However, given that thebottle-shaped can 1 thus having the defects at the micro level on thethermoplastic resin coating layer is filled with wine having strongmetal corrosive properties such as champagne or sparkling wine etc., thebottle-shaped can 1 will be corroded at the defected portions of thethermoplastic resin coating layer, and flavor of the content maydeteriorated by such corrosion.

An amount of sulfurous acid to be added to wine during fermentation isdefined by Japanese food sanitation act in manner such that sulfurousacid will not remain more than 350 mg per 1 kg (i.e., 350 ppm) of wine.However, sulfurous acid has strong metal corrosive properties to corrodethe metal can. Therefore in order to prevent the metal can in storagefrom being corroded, and to prevent flavor of the content from beingdeteriorated by hydrogen sulfide resulting from a reaction betweensulfurous acid and the metal body, calcium carbonate has been added to aprotection layer covering the inner surface of the can for the purposeof trapping sulfurous acid.

Even if the protection layer has such defects at the micro level,sulfurous acid gas is captured by calcium carbonate contained in theprotection layer (i.e., the thermoplastic resin layer or an adhesivelayer). Therefore, the metal sheet forming the bottle-shaped can willnot be corroded by still wine that does not contain carbonic acid.However, if the bottle-shaped can is filled with sparkling wine havingstrong metal corrosive properties, carbon dioxide is produced inaddition to sulfurous acid gas. The carbon dioxide thus producedpenetrates into the protection layer from the defects at the micro leveland reacts to calcium carbonate in the protection layer. As a result,trapping efficiency of calcium carbonate to capture sulfurous acid gaswill be degraded or deteriorated. Therefore, the metal sheet forming thebottle-shaped can will be corroded by both sulfurous acid gas and carbondioxide, and flavor of sparkling wine will be deteriorated by hydrogensulfide resulting from a reaction between sulfurous acid gas and themetal material of the bottle-shaped can. Thus, the bottle-shaped can hasnot yet been used to hold sparkling wine.

In order to solve above-explained disadvantage, according to thepreferred example, the bottle-shaped can 1 for holding sparkling winehaving strong metal corrosive properties is manufactured without usingcapturing agent such as calcium carbonate more than necessary. To thisend, the thermoplastic resin coating layer covering the inner surface ofthe bottle-shaped can 1 is heated and cooled rapidly at an inner surfaceof the annular beads 14 and 15 at an amorphization step to reducecrystallinity degree of the thermoplastic resin coating layer on theinner surface of the annular beads 14 and 15 to be lower than that onthe inner surface of the can trunk 2. Therefore, the plastic deformationof the annular bead, and deterioration in soundness of the inner coatinglayer of the annular beads 14 and 15 resulting from the curling,threading and bead forming steps, are recovered before the bottle-shapedcan 1 shown in FIG. 1 is finished.

Metal sheet material for the bottle-shaped can 1 is not limited tospecific material. For example, a black plate, a phosphate treated steelsheet, an electrolytic chromate treated steel sheet, an aluminum sheet,a chromate treated aluminum sheet, an aluminum alloy sheet and so on aresuitable for forming the bottle-shaped can 1. Above all, the aluminumalloy sheet of 3004 series having a thickness of 0.2 mm to 0.32 mm isespecially suitable. If the thickness of the metal sheet is thinner than0.2 mm, buckling strength against capping pressure cannot be ensured. Bycontrast, if the thickness of the metal sheet is thicker than 0.32 mm,the buckling strength can be ensured sufficiently but it is tooexpensive.

In the preferred example, the thermoplastic resin film made of polyesterresin, polypropylene resin or the like can be used to form the coatinglayer for covering the inner surface of the can body. The polyesterresin includes: a homopolymer such as polyethylene terephthalate,polybutylene terephthalate, polyethylene isophthalete etc.; a copolymerprepared by mixing polyethylene terephthalate with polyethyleneisophthalete; and a blending resin consisting of copolymers orconsisting of the homopolymer and the copolymer. In addition, thethermoplastic resin film may be formed not only into a single layer butalso into a multiple layer.

A thickness of the resin film is preferably within a range of 10 to 50μm. Specifically, the thickness of the resin film formed on the face ofthe metal sheet to be the inner face of the can body is determined toprevent a corrosion of the can body after subjecting the bottle-shapedcan 1 to the roll-on capping. That is, if the thickness of the resinfilm is thinner than 10 μm, it would be difficult to ensure thecorrosion resistance against the content having strong metal corrosiveproperties after subjecting the bottle-shaped can 1 to the roll-oncapping. By contrast, if the thickness of the resin film is thicker than50 μm, the corrosion resistance can be ensured sufficiently but it istoo expensive. Therefore, the thickness of the resin film is limitedwithin the range of 10 to 50 μm, preferably within the range of 12 to 40μm to ensure quality of the film while justifying cost economy.

Optionally, additives such as antioxidant, thermostabilizer,plasticizer, lubricant may be added to the resin layer. In addition,according to the preferred example, the capturing agent such as calciumcarbonate is added to the resin film to react to sulfurous acidcontained in wine, except for a region to be contacted with a jig.Therefore, sulfurous acid contained in wine will not penetrate throughthe coating layer to cause a corrosion of the metal sheet forming thebottle-shaped can 1. In addition, flavor of wine will not bedeteriorated by hydrogen sulfide resulting from a reaction betweensulfurous acid and the metal sheet. Here, an additive amount of calciumcarbonate may be determined in accordance with an amount of sulfurousacid contained in wine.

The thermoplastic resin film may be bonded directly to the metal sheetby a thermal bonding method. Otherwise, the thermoplastic resin film maybe bonded directly to the metal sheet by extruding a meltedthermoplastic resin in a T-die onto the preheated metal sheet.Alternatively, a preformed thermoplastic resin film may also be bondedto the metal sheet by a thermal bonding method through an adhesiveprimer layer, a curable adhesive layer, or a thermally adhesivethermoplastic resin layer.

A closure (not shown) applied to the bottle-shaped can 1 is abottomed-cylindrical metal member comprised of a ceiling and a skirtportion. Specifically, the bottle-shaped can 1 is filled with thecontent from the container mouth 4, and the closure is applied to thecontainer mouth 4. Then, a roll-on capping is carried out using theconventional capping apparatus while pressing the ceiling. In thissituation, the skirt portion of the closure is threaded by a threadingroller and a lower end (i.e., an opening end) of the skirt portion istightened by a tightening roller.

Material of the closure is not limited to specific material, but A1100alloy or A3105 alloy defined by JIS are especially suitable. Inaddition, an inner face of the closure is coated with an epoxy-phenolresin or the like.

Further, a resin sealing liner is affixed to the inner face of theceiling. The closure is resealable even after unscrewed, and apilfer-proof band is attached to the lower end of the skirt portionthrough bridges. Therefore, the pilfer-proof band remains around thecontainer mouth after the closure is unscrewed to proof a fact that theclosure has been opened. That is, the pilfer-proof closure has atamper-proof function.

As described, the closure is applied to the container mouth 4 from aboveafter filling the bottle-shaped can 1 with the content, and a cappingpressure is applied to the ceiling of the closure. Then, a female threadis rolled on the skirt portion of the closure along with the male thread13 of the container mouth 4 by the threading roller while pressing theceiling. In this situation, as shown in FIG. 4, a lower end 23 of theskirt portion 22 is pushed onto the inclined face 14 a of the convexbead 14 by the tightening roller 21. As a result of thus threading andtightening the closure applied to the container mouth 4 by the roll-onmethod, the annular beads 14 and 15, especially the inclined face 14 amay be deformed to have an oval or elliptical cross-sectional shape orthe like by a lateral load applied by the tightening roller 21. As alsodescribed, the thermoplastic resin film covering the inner surface ofthe container mouth 4 is amorphized at the annular beads 14 and 15. Suchamorphization is closely related to a capping pressure, an impact of theroller, and the lateral load. Such relation will be explained in moredetail.

The amorphization is also carried out before the foregoingcurling/threading/beading step, by heating the bottle-shaped can 1entirely. However, at the amorphization step of the preferred example,the container mouth 4 is heated locally (e.g., by high-frequencyinduction heating method) to amorphize the thermoplastic resin coatinglayer covering the inner surface of the annular beads 14 and 15.Consequently, the thermoplastic resin coating layer thus amorphized isallowed to flexibly cover the inner surface of the annular beads 14 and15 even if the annular beads 14 and 15 are deformed into an oval orelliptical shape or even if the container mouth 14 is diametricallyshrunk by the impact or lateral load of the tightening roller 21 at theroll-on capping. For example, at the amorphization step, ahigh-frequency induction heating device may be used to heat thecontainer mouth 4 locally. Alternatively, other conventional heatingmeans such as an electric furnace, a gas oven, an infrared heatingdevice etc. may also be used.

In order to prevent corrosion of the metal sheet by carbon dioxide andsulfurous acid, various kinds of experimentations have been conducted.As a result of the experimentations, it was found that the corrosion ofthe metal sheet can be prevented effectively by amorphizing thethermoplastic resin inner coating layer by locally heating and coolingthe container mouth 4. However, in order to curb the influence of asoftening of the metal material and a thermal history of thethermoplastic resin inner coating layer, it is preferable to cover theshoulder portion 3 by a shield or the like to reduce an impact of heat.

According to the preferred example, therefore, the roll-on capping canbe applied to the container mouth without damaging the thermoplasticresin inner coating layer. For this reason, the inner surface of thebottle-shaped can 1 can be prevented from being corroded by a gaseouslayer in a head space of the bottle-shaped can 1, that is, by carbondioxide and sulfurous acid contained in sparkling wine having a highacid level (i.e., low ph level) and strong metal corrosive properties.

The amorphization step will be explained in more detail. At theamorphization step, first of all, the annular beads 14 and 15 are heatedby the high-frequency induction heating method until a temperature ofthe thermoplastic resin coating layer covering the inner surface of theannular beads 14, 15 is raised to a melting point thereof or higher.Consequently, the thermoplastic resin coating layer is melted at leaston the inner surface of the annular beads 14, 15. After thethermoplastic resin is brought into non-orientation state, thebottle-shaped can 1 is turned upside down to orient the container mouth4 downwardly to dip the container mouth 4 in the water held in a coolingtank. To this end, pure water at a temperature lower than acrystallization temperature of the thermoplastic resin is held in thecooling tank. As a result, the container mouth 4 is cooled rapidly andthe thermoplastic resin coating layer is amorphized melted at least onthe inner surface of the annular beads 14, 15. Then, water adhering tothe container mouth 4 is blown off by air. In this preferred example, adegree of amorphization of the thermoplastic resin film covering theinner surface of the bottle-shaped can 1 is measured by measuring acrystallinity of the thermoplastic resin film by an IR spectroscopymethod (reflection infrared spectroscopy method).

Specifically, in order to measure a crystallinity of the thermoplasticresin coating film, the container mouth 4 is immersed in a hydrochloricsolution of about 8 percent concentration to isolate the thermoplasticresin inner film from the inner surface of the container mouth 4. Then,absorption peak of polyethylene terephthalate is individually obtainedat 1340 cm⁻¹ and at 1578 cm⁻¹ by measuring the crystallinity of an innersurface of the thermoplastic resin film contacted with the content by anATR method (i.e., an attenuated total reflection method).

According to the preferred example, the thermoplastic resin coating filmcovering the inner surface of the annular beads 14, 15 is amorphized toreduce the crystallinity (Cn) thereof to be lower than 1, as expressedby the following inequality:

Cn<1  (1).

In the above inequality (1), the crystallinity Cn is an infraredabsorption intensity measured by IR spectroscopy method, which can beexpressed by the following expression:

Cn=(a peak height at 1340 cm⁻¹)/(a peak height at 1578 cm⁻¹).

In addition, the corrosion resistance of the thermoplastic resin coatingfilm covering the inner surface of the container mouth 4 after cappingcan be further enhanced while maintaining the buckling strength againstthe capping pressure, by amorphizing the thermoplastic resin coatingfilm in such a manner that the crystallinity (Cn) of the thermoplasticresin coating film at the inner surface of the container mouth 4 isreduced to be lower than a crystallinity (Cw) of the thermoplastic resincoating film at the inner surface of the can trunk 2, as expressed bythe following inequality:

Cn/Cw<1  (2).

In the above inequality (2), the crystallinity Cw is an infraredabsorption intensity measured by IR spectroscopy method, which can beexpressed by the following expression:

Cw=(a peak height at 1340 cm⁻¹)/(a peak height at 1578 cm⁻¹).

In order to interfere with the development of microorganisms thatcompromise the safety of the content, the temperature of the purecooling water held in the cooling tank is maintained within the rangefrom 50 to 70° C., while circulating the cooling water. Most of themicroorganisms causing food intoxication are propagative within atemperature range of 10 to 37° C. therefore, in the preferred example, atemperature of the cooling water in the tank is kept to be lower than50° C. By contrast, there are also microorganisms inhabitable at atemperature higher than 85° C., and an inhabitation of suchmicroorganisms can be prevented by keeping the temperature of thecooling water lower than 70° C.

At the amorphization step, the cooling water is allowed to be introducedeasily into the container mouth 4 by lowering the container mouth 4 intothe cooling water while inclining. In this case, the container mouth 4is pulled out of the water tank while being inclined inversely so thatthe cooling water can be introduced and discharged to/from the containermouth 4 without resistance of air.

In order to introduce the cooling water further smoothly into thecontainer mouth 4, the cooling water is circulated in the tank at a(substantially) same speed as the conveying speed of the bottle-shapedcan 1 in the same direction as the conveying direction of thebottle-shaped can 1. In addition, the resistance of the cooling watercan be reduced so that the container mouth 4 is pulled out of the tankwhile discharging the cooling water without ruffling the cooling waterin the tank. Therefore, the bottle-shaped can 1 is allowed to beconveyed stably in the cooling water held in the tank even if a weightof the bottle-shaped can 1 is light.

According to the preferred example, the necking and flanging of thelower end of the can trunk 2 is carried out after thecurling/threading/beading steps, and then the bottom lid is seamed withthe lower end of the can trunk 2. Therefore, the bottle-shaped can 1 isallowed to be held tightly from both sides without causing a deformationof the thinned can trunk 2 so that the bottle-shaped can 1 is rotatedaround its axis in a stable manner to heat the annular beads 14 and 15homogeneously by the high-frequency induction heating device.

As described, the container mouth 4 is inclined when lowered into thecooling water so that the cooling water is introduced smoothly into thecontainer mouth 4 while removing air from the bottle-shaped can 1.Therefore, the container mouth 4 can be cooled rapidly. Likewise, thecontainer mouth 4 is inclined inversely when pulled out of the watertank so that the cooling water is discharged smoothly from the containermouth 4 without causing a pulsation of the cooling water. Therefore, thecooling water can be removed easily from the container mouth 4.

As also described, the cooling water is circulated in the tank at asubstantially same speed and in the same direction as those of thebottle-shaped can 1 being conveyed while being turned upside down.Therefore, the cooling water is allowed to be introduced smoothly intothe container mouth 4 and the container mouth 4 is allowed to be pulledout of the tank while discharging the cooling water without ruffling thecooling water in the tank. Therefore, the bottle-shaped can 1 can beconveyed stably in the cooling water held in the tank even if a weightof the bottle-shaped can 1 is light.

Experimentation

Resin Coated Metal Sheet

In this experimentation, an aluminum alloy sheet of A3004H19 serieshaving a thickness of 0.285 mm and AB poof stress of 270 N/mm² was usedas the metal sheet. Each surface of the metal sheet were coveredindividually with a film made of mixed resin (PBT:PET=60:40) ofpolybutylene terephthalate (PBT) and polyethylene terephthalate (PET)having a thickness of 20 μm. Here, the resin film was formed on the faceof the metal sheet to be the inner face of the can through an adhesiveagent such as epoxy resin containing calcium carbonate.

Manufacture of the Bottle-Shaped can

At the cup shaping step, the disc-shaped blank was punched out from theabove-explained metal sheet covered with the polyester resin coating,and then shaped into the cup having a height of 42 mm and a diameter of95 mm by the drawing treatment. The side wall of the cup thus preparedwas subjected to the drawing and ironing (total ironing rate: approx.40%). The open end of the can was trimmed to realize a constant height,and the closure member was further shaped into a bottomed cylindricalmember having a trunk diameter 59 mm and a height of 142 mm. Then, abottom side of the bottomed cylindrical member was subjected to the topdoming, and an intermediate body of the bottle-shaped can 1 having aheight 174 mm was finished (the upper end had not yet opened).

The lubricant was removed from the intermediate body, and theintermediate body was subjected to the amorphizing treatment of theresin film. Then, a closed face of the container mouth 4 was cut off toopen the container mouth 4, and the open end portion 11 of the containermouth 4 was curled outwardly to form the curled portion 12. After that,the male thread 13 to be engaged with the female thread of the closurewas rolled on container mouth 4 below the curled portion 12, and theannular beads 14 and 15 were formed below the thread 13.

In the container mouth 4 (having outer diameter of 28 mm), thus formed,an outer diameter of the convex bead 14 was 28 mm, an outer diameter ofthe concave bead 15 was 25.9 mm, and an inclination of the inclined face14 a was formed between the beads 14 and 15 was 45°.

Specifically, number of ridges of the male thread 13 formed around thecontainer mouth 4 was 8 ridges/inch.

Consequently, a can body in which the curled portion 12, the thread 13,and the annular beads 14 and 15 are formed on the container mouth 4 wasprepared. Then, the necking was applied to the lower open end portion ofthe can trunk 2 on the opposite side of the container mouth 4, and theseparate bottom lid 5 made of metal sheet covered by the thermoplasticresin films on both sides was seamed to the flange portion of the loweropening of the can trunk 2 by a double-seaming method.

The can body was then passed through a high-frequency induction heatingapparatus within a short period while being rotated multiple times.Consequently, a temperature of the can body was raised to a rangebetween 265° C. and 300° C.

In the high-frequency induction heating apparatus, induction heatingcoils were arranged above a conveyor on both sides of the containermouth 4 of the can body at the same level to locally heat the containermouth 4. To this end, a heat-resistant grip belt conveyor was used toconvey the can body. The belt conveyor was adapted to rotate the canbody more than four times during passing the can body through theheating apparatus. Therefore, the container mouth 4 was allowed to beheated to 265° C. to 300° C. locally and homogeneously within severalseconds even if conveying the can body at a speed higher than 30 m/min.In addition, a radiation thermometer was arranged at an outlet of thehigh-frequency induction heating apparatus to measure the temperature ofthe can body coming out of the heating region, and a high-frequencytransmitter was provided to output a measurement result (those elementsnot shown). The system thus structured were controlled electrically sothat the temperature of the can body was allowed to be raised certainlyto a desired temperature even if the conveyor speed was changed. In caseof conveying the can body using a turret, an arrangement of thehigh-frequency induction heating apparatus may be changed flexibly toconform to a configuration of a conveying passage.

In order to rapidly cool the container mouth 4 thus heated, coolingwater at a temperature within a range of 60° C. plus or minus 10° C. wasprepared in a cooling tank. The can body was then transported to thecooling tank within a short time (within 3 seconds, in thisexperimentation) after coming out of the outlet of the high-frequencyinduction heating apparatus, and the container mouth 4 whose temperaturewas lowered approximately to 200° C. was immersed in the cooling water.As a result, the thermoplastic resin coating layer was amorphized atleast on the inner surface of the annular beads 14, 15 so that thedefects of the resin coating layer at the micro level caused duringforming the container mouth 4 was recovered. After thus amorphizing theresin coating layer covering the inner surface of the container mouth 4,water adhering to the container mouth 4 as blown off. As a result, thebottle-shaped can 1 was finished. In the finished bottle-shaped can 1 awall thickness of the concave bead 15 was 0.285 to 0.36 mm, a hardnessof the concave bead 15 was Hv 84 to 88 (Hv 92 to 96, before beingprocessed), a height of the bottle-shaped can 1 was 162 mm, and acontent of the bottle-shaped can 1 was 300 ml. It was confirmed that thedegree of the amorphization of the inner coating layer on the containermouth 4 was higher than that on the can trunk 2.

In the experimentation, a crystallinity (Cn) of the thermoplastic resincoating layer at the inner surface of the container mouth 4 wasmeasured, and it was 0.25. In the experimentation, a mixed resin ofpolybutylene terephthalate (PBT) and polyethylene terephthalate (PET)was also used to cover the inner surface of the container mouth 4instead of the polyethylene terephthalate resin layer. In this case, acrystallinity (Cn) of the amorphized resin coating layer at the innersurface of the container mouth 4 was 0.75. Thus, the crystallinities(Cn) of both resin layers at the inner surface of the container mouth 4were less than 1.

The bottle-shaped can 1 thus prepared was filled with corrosionpromotion liquid for sparkling wine (composition; carbonated water 270g, ethanol 30 g, citric acid 1.5 g, potassium metabisulfite 60 mg), anda closure was applied to the container mouth 4 by the roll-on cappingmethod, with a capping pressure of 80 kgf and a threading roller torqueof 3.0 Nm. The bottle-shaped can 1 thus filled with the content wasstored in an upright manner for 1.3 month at room temperature of 38° C.However, no abnormality was found on the surface of container mouth 4(including the curled portion 12, the thread 13, and the annular beads14 and 15) even after the storage.

As a comparative example, another can container which was not subjectedto the amorphizing treatment of the container mouth (a crystallinity(Cn) of the thermoplastic resin coating layer at the inner surface ofthe container mouth was 1 to approx. 1.5) was filled with the samecontent, and closed by the roll-on capping method. The can container ofthe comparative example was also stored and assessed by the same manner.In this case, damage of the film at the inner surface of the annularbeads (i.e., defects at the micro level) was not reduced even if thelateral load of the tightening roller was reduced, and a corrosion ofthe metal material was confirmed. On the contrary, scarcely anycorrosion of the container was found if the container was not subjectedto the tightening of the closure by the tightening roller.

The present invention should not be limited to specific example thus farexplained, for example, various kinds of surface treated metal sheetsfor forming a can such as a metal plated steel sheet and a chemicalconversion coated steel sheet such as a TFS sheet may also be usedinstead of the aluminum alloy sheet. Thus, the a metal sheet may beselected arbitrarily from the above-explained surface treated metalsheets and steel sheets depending on the content while taking intoconsideration the corrosion resistance.

In the above experimentation, the blending resin consisting of PET andPBT was used to form the thermoplastic resin film. However, thethermoplastic resin is also not limited to the blending resin. Forexample, copolymers such as PET, or a mixed resin consisting of thehomopolymers or a mixed resin consisting of the copolymer andhomopolymer may also be used.

As described, according to the preferred example, the resin filmcovering the inner surface of the container mouth 4 is amorphized afterforming the container mouth 4 as expressed by the inequality (1).However, if the crystallinity of the thermoplastic resin coating layerat the inner surface of the container mouth 4 is smaller than 1 evenwithout amorphizing, the amorphization steps of the thermoplastic resincoating layer at the container mouth 4 may be omitted. For instance, thecrystallinity of the thermoplastic resin coating layer at the innersurface of the container mouth may be lowered to be smaller than 1 byadding copolymerization component to the resin composition to delay acrystallization velocity, or by blowing cooling air of low temperaturecompulsory to the container mouth at the heating/cooling step afterforming the container mouth.

In the preferred example, the amorphization steps are carried out afterthe can lid seaming step. For example, the amorphization steps may alsobe carried out after the curling/threading/beading steps before the canlid seaming step. However, stiffness of the can trunk 2 can be enhancedby seaming the bottom lid 5 to the can trunk 2. Therefore, the can trunk2 will not be deformed even if held by the belts of both sides whilebeing rotated by running those belts in opposite directions when heatingthe container mouth 4. That is, the container mouth 4 can be heatedhomogeneously by the high-frequency induction heating apparatus. Thus,it is desirable to carry out the amorphization steps after the can lidseaming step to heat the container mouth 4 homogeneously and conveyingthe bottle-shaped can 1 at high speed.

Given that can body is has a sufficient buckling strength against thecapping pressure, the container mouth 4 including the curled portion 12,the thread 13, and the annular beads 14 and 15 is allowed to be heatedentirely. However, the thermoplastic resin on the container mouth 4 isdamaged most seriously at the portion other than the annular beads 14and 15 within the region contacted with leading end of the roller at theroll-on capping. Therefore, it is desirable to amorphize thethermoplastic resin film by heating only the annular beads 14, 15 andvicinity thereof to prevent the can trunk 2 from being thinnedexcessively and to prevent the thermoplastic resin film from beingweakened by the thermal history.

The container mouth 4 may be cooled not only by being immersed in thecooling water as described in the preferred example but also by blowingthe cooling water or cooling air thereto.

In the preferred example, the present invention is applied to thebottle-shaped can in which the bottom lid is seamed to the lower end ofthe can trunk. However, the present invention may also be applied to acan body in which the shoulder portion and the container mouth areformed by diametrically reducing an open end side of the cylindrical canbody, and in which the can trunk and the bottom lid are formedintegrally (i.e., to a monoblock type can body).

Besides, a manufacturing method taught by an international publicationWO01/015829 is suitable for manufacturing a bottle-shaped can having anelongated container mouth. Therefore, flexibility in the shape of thecan may be improved by using the manufacturing method taught by aninternational publication WO01/015829, in comparison with a case offorming the monoblock type by the conventional method.

Lastly, it is also possible to attach a printed shrink to the can trunk2 of the bottle-shaped can 1 instead of printing on the can trunk 2.

1. A bottle-shaped can manufacturing method, comprising: a cup shapingstep of forming a cup by punching out from a metal sheet in which athermoplastic resin coating layer is formed on at least a surface to bean inner face of the can and a lubricant is applied thereto; a can trunkshaping step of shaping the cap into a diametrically reduced bottomedcylindrical can body; a container mouth shaping step of forming ashoulder portion and a container mouth by diametrically reducing one ofthe end portions of the bottomed cylindrical can body; acurling/threading/beading step of forming a curled portion on a leadingend of the container mouth, and forming a thread and an annular bead onthe container mouth; and an amorphization step of amorphizing at leastthe thermoplastic resin coating layer covering an inner surface of thecan body in which the curled portion, the thread and the annular beadare formed on the container mouth situated above the shoulder portion,by heating at least the thermoplastic resin coating layer covering theinner surface of the can body to above a melting point thereof, andimmediately cooling the heated thermoplastic resin coating layer.
 2. Thebottle-shaped can manufacturing method as claimed in claim 1, whereinthe container mouth shaping step includes a top dome shaping step offorming the shoulder portion and the container mouth by diametricallyreducing a bottom side of the bottomed cylindrical can body; and whereinthe amorphization step includes a step of amorphizing at least thethermoplastic resin coating layer covering the inner surface of the canbody in which the container mouth is opened and a bottom lid is seamedto a lower end of the can trunk on the side opposite to the containermouth.
 3. The bottle-shaped can manufacturing method as claimed in claim1, wherein the amorphization step includes: an induction heating step ofletting the can body through an induction heating apparatus whilerotating the can body around an axis of the can; and a cooling step ofimmediately cooling the heated container mouth by immersing thecontainer mouth into a cooling water held in a cooling tank.
 4. Thebottle-shaped can manufacturing method as claimed in claim 3, whereinthe cooling step includes a step of cooling the container mouth byimmersing the container mouth into the cooling water held in the coolingtank while orienting the container mouth downwardly; and wherein theamorphization step includes a blowing step of blowing off the wateradhering to the container mouth oriented downwardly.
 5. Thebottle-shaped can manufacturing method as claimed in claim 3, whereinthe amorphization step includes a cooling step of cooling containermouth of the can body conveyed in a manner to orient the container mouthdownwardly, by immersing the container mouth into the cooling water heldin the cooling tank while inclining a center axis of the container mouthwith respect to a water surface, and thereafter pulling the containermouth out of the cooling tank while inclining the container mouthinversely to that of the case of immersing the container mouth into thecooling water.
 6. The bottle-shaped can manufacturing method as claimedin claim 3, wherein the amorphization step includes a cooling step ofcooling container mouth while circulating the cooling water in the tankat a substantially same speed as a conveying speed of the can body andin the same direction as a conveying direction of the can body.
 7. Abottle-shaped can, that is formed from a metal sheet in which athermoplastic resin coating layer is formed on at least a surface to bean inner face of the can, wherein a crystallinity (Cn) of thethermoplastic resin coating film covering an inner surface of acontainer mouth of the finished can satisfies a following inequality(1):Cn<1  (1); where Cn is an infrared absorption intensity measured by IRspectroscopy method (reflection infrared spectroscopy method), which canbe expressed by a following expression:Cn=(a peak height at 1340 cm⁻¹)/(a peak height at 1578 cm⁻¹).
 8. Thebottle-shaped can as claimed in claim 7, wherein a relation between thecrystallinity (Cn) of the thermoplastic resin coating film at the innersurface of the container mouth of the finished can, and a crystallinity(Cw) of the thermoplastic resin coating film at an inner surface of thecan trunk satisfy a following inequality (2):Cn/Cw<1  (2); where Cw is an infrared absorption intensity measured bythe IR spectroscopy method (reflection infrared spectroscopy method),which can be expressed by a following expression:Cw=(a peak height at 1340 cm⁻¹)/(a peak height at 1578 cm⁻¹).
 9. Thebottle-shaped can as claimed in claim 7, wherein the thermoplastic resincoating layer covering an inner surface of the container mouth issubjected to an amorphization treatment to amorphize the thermoplasticresin after forming the container mouth, by heating the thermoplasticresin coating layer to above a melting point thereof, and immediatelycooling the heated thermoplastic resin.